You're welcome Stu. Here's some important notes that should receive serious consideration.
(1) The circuit as it's currently drawn has the ability to adjust the control (input) voltage to 0V when the Pot is turned to its fully clockwise extreme.
(2) The circuit I drew assumed that an increase in control (input) voltage produces a longer PWM on time, thus increasing motor speed.
(3) Keeping notes 1 & 2 in mind I drew my pictorials where turning the Pot clockwise will reduce motor RPM because this would be the intuitive direction to increase water temperature.
Earlier in this thread I stated that I have no idea if increasing the control voltage translated into increasing PWM (On Time) that will translate to increasing RPM. That was the post that I commented on deciphering Chinese tech data.
I just went back to the Ebay link and looked at the photo that includes the Pot plugged into the board. Keeping in mind that turning the Pot clockwise to increase RPM is intuitive (except for women
) my circuit's analog logic may be backward. This is because we never did determine if an increase in control voltage translates to increase in RPM. Looking at that Photo tells me the opposite is true.
So what's the bottom line?
As with all prototyping design nothing should be considered final and permanent unit
all experimentation is completed and you're satisfied with the results. This means all connections should be only tacked soldered until final design. Live circuit tests should be done prior to stuffing everything in an enclosure.
I would suggest that you experiment with a with a 12V or 24V incandescent lamp (torch) as a load with the Pot wiring unmodified. Then measure the control voltage between GND (Black) and Pot's wiper (White) while turning the Pot clockwise and counter clockwise while also observing the brilliance of the lamp.
On a final note I would not recommend using your boat's storage cells as a supply for prototyping. They're WAAAAAY to powerful and totally unforgiving if you have an "Oh Sh!T!" moment. A 12VDC wallwart plugged into shore power would be sufficient for experimental prototyping. Even a little 9V battery and low current lamp load would suffice for testing. I guess an LED with a 330Ω series resistor should work for a load too but incandescent lamps respond to PWM better and are more easily seen by the human eye.
Lets us know when you start your experiments.
Alec, take a look at this photo. Assuming clockwise rotation increases pulse width do you agree that this looks like decreasing control voltage increases pulse width?
Chris